Thermostat for electrical fire-alarm systems



Feb. 12 1924. I 1,483,787 T. s. DIXON THERMOSTAT FOR ELECTRICAL FIRE AIQARI SYSTEMS Filed May a, 1922 Patented Feb. 12, 1924.

1,483,787 PATENT OFFICE.

UNITED STATES THOMAS STOKEB DIXON, OF CHRISTCHURCH, HEW ZIALLND, ASSIGNOB TO THE 7161- LAIIT AUTOMATIC FIRE ALABH COMPANY LIIITED, OI CHRISTCHURCH, HEW ZEL- LAND, A COMPANY OI NEW MAID.

THEBKOSTAT FOB HLECTBICAL nan-emu SYBTEHS.

Application ma lay a, 1922. Serial Io. mass.

T all whom it may concern:

' Be it known that I, Tnouas S'rom DIXON, a subject of the King of Great Britain and Ireland, residin in Christ- 6 church, in the Dominion of ew Zealand,

have invented a new and useful Improvement in Thermostats for Electrical Fire- Alarm Systems; and I do hereby declare the following to be a full, clear, and exact 10 description of the same.

This invention relates to thermostats for automatic electrical fire alarm systems of the class in which an open circuit has alternative lines and a return path, the

ll open circuit being' normally completed from one alternative line and if heating continues such circuit will also be comleted from the other alternative line, and

, in which upon the expansion of a tube,

90 a rod within the tube is moved backwards and operates an arm adapted to make and break contact wit-h electrical contacts.

One object of the invention is to provide an arrangement whereby the loss of motion caused by the difliculty of fittin at the pivot of the thermostat arm is need to a minimum.

It has also been found in thermostats of the above class where the two open circuit contacts were located upon the one side of the flexible leaf that after'the leaf touched the second open circuit contact and heating still continuing, the leaf would be caused to leave the open circuit contact and so break such circuit. One of the objects of this invention i to obviate this disadvantage and to ensure a better and closer contact being made.

The invention is illustrated in the ac- 40 companying drawings, wherein Figure 1, is a view showing the thermostat in position.

Figure 2, is a plan with the cover of the thermostat removed. Figure 3, is an enlarged plan of one end of the thermostat.

Figure 4, is a sectional mentary view of a part of the other on of the thermostat. Figure 5, is a sectional elevation of the portion shown in Figure 3.

Figure 6, is an end view of the thermostat.

the two 0 a 'correspon ingly shaped recess in a memher 6 fixed to the thermostat arm 7, the said thermostat arm 7 consisting of a blade of spring material fixed to the shoulder 8 of t e wall 3. by screws, 9. Such arm 7 is set in such a position that tension thereof will be exerted against the rod 4 within tube. The member 6 in which the rod engags is fixed to the thermostat arm 7 at su a position on the blade that the travel of the end of the blade will be suf ficiently multi lied to provide the required movement an yet be sufficiently sensitive 'tobe acted upon by therodassuchrod moves imder the action of the tube. As the tube expands by heat the rod 4 will move ,backwards and permit the blade 7 under its own tension to move in the direction of the arrow in Figure 2. The end of the thermostat arm 7 is provided with a s ring leaf 10 attached to the end of the lade 7 and is normally heldin contact with a closed circuit contact 11 while the open circuit contact 12 rejects from a member 13 arranged u on t e opposite side of the leaf to that of t e closed circuit contact. 11.

By arranging the contacts in this way only two contacts are required. Where three contacts have been employed in this ty e of device, the closed circuit contact being located upon one side of the leaf and n circuit contacts upon the other side of t eleaf, it was found that after the leaf touches the second open circuit contact and heat still continuing the leaf would be caused to leave the first open circuit contact and so break the circuit. In the present invention, however, the closed circuit contact takes the place of the second open circuit contact employed in the type referred to and after the leaf has v touched the open circuit contact 12 further movement of the blade 7 in the direction of the arrow will cause the front end of the leaf to bend, as shown in Figure 7, and its front end again to touch with the closed circuit contact 11 and further movement of the blade will only tend to increase the contact of the leaf against the contacts 11 and 12. The closed circuit contact 11 is mounted in an extension 14 of a terminal 15 insulated from the end wall 16 of the thermostat by plugs ,17 of insulating material.

The contact 12 is mounted in an extension 13 of a terminal 19 which is mounted in the end wall 16 but insulated from the end wall by plugs 18. The leaf is connected with the terminal 20, which is located in but insulated from the end wall 16, by means of a flexible cord 21 leading from the inner end of the terminal 20 to a pin 22 which secures the leaf 10 to the arm 7. The pin is, therefore, in electrical contact with the leaf 10 but is insulated from the blade 7.

The ends of the wires for the closed circuit are respectively connected to the tenninals and and the leaf 10 normally rests against the contact 11 as shown in Figure 3, thus completing the closed circuit from one terminal 14 to the other terminal 20 of the closed circuit through the blade 10 and flexible cord 21. The tube 1 may be of any suitable metal having a greater coefiicient of exansion than the rod.4 and as the rod is fixed to the outer end of the tube, the latter, when heat is applied'thereto, is caused to expand thereb moving the rod whereby the free end 0 the arm 7 will travel in the direction of the arrows shown in the Figures 2 and 3. During this primitive movement of the arm 7, the blade 10 carried thereby will be brought into contact with the member 12, thereby completing the electrical circuit in which is included the terminals 19 and 20, this electrical circuit having included therein a suitable signalling device or annunciator. As the heat upon the tube 1 increases a greater expansion takes place causing the further movement of the rod 4,

which in turn, increases the pressure upon the arm 7 until the blade 10 contacts with the members 11 and 12 as is illustrated in Fi re 7. The contact member 12 acts as a lcrum for the blade 10, causing the free end thereof to contact with the member 11 and for any unforeseen reason a circuit is not completed from the terminal 20 to the terminal 19, a circuit will becompleted from the terminal 15 through the contact 11 to the contact 12 and to the terminal 19 through the conductors as hereinafter described.

The wall of the tube 1 is reduced in thicknose for the greater length thereof in order to render it more sensitive to a change of temperature.

It will be noticed that the end walls 2 and 16 are made circular so that the whole thermostat may be enveloped by a sleeve 24 which is passed over the tube and butts against a flange 25 upon the end wall 16. A cap 26 is screwed upon the end wall 16 to enclose the terminals pro'ecting from the end wall 16. A band 27 1s adapted to encircle the sleeve 24 and has flanges 28 for securing it to a ceiling or wall. A screw 29 passes through the neck of the band for tightening the band upon the sleeve and thus securing the thermostat firmly in position (see Fi ures 1 and 8). For inspection purposes tfie screw 29 is relaxed enabling the sleeve to be passed off the base on to the tube 1 (see dotted lines in Figure 1,) and the mechanism of the thermostat inspected without removing the thermostat from its position. The bush 30 in the outer end of the tube 1 is slotted as shown in order to tighten the bush upon the threaded end of the rod in case of wear.

What I claim is 1. In an electrical fire alarm thermostat having an arm operable by the heating of the thermostat, a flexible leaf upon the end of said arm adapted to rest against a closed circuit contact in order normally to complete a closed circuit and in which upon heating of such thermostat such leaf will leave such closed circuit contact and will touch open circuit contacts in order to complete an open circuit from alternative lines; means, charac terized in this, that said closed circuit contact also forms one of the open circuit contacts, said other open circuit contact located upon the other side of the said leaf at such a position in relation to the said closed circuit contact as to form a fulcrum for the leaf whereby as the thermostat arm continues moving after the leaf touches the first contact the front end of the leaf will bend so as to again touch the second contact, substantially as described.

2. In an electrical fire alarm thermostat having an arm operable by the heating of the thermostat, a flexible leaf u on the end of said arm adapted alternate y to touch open circuit contacts in order to complete an open circuit from alternative lines; means, characterized in this, that one of said contacts is located upon the one side of said leaf and the other contact upon the other side of said leaf, the first mentioned contact being at such a position that it will form a fulcrum for the leaf whereby if the thermostat arm continues moving after the leaf touches the first contact the front end of the leaf will bend so as to again touch the second contact, substantiall as described.

3. In an electric fire a arm thermostat having an arm operable by heating of'the thermostat and a flexible leaf upon the end of said arm said leaf adapted to rest against eans? ,a closed circuit contact in order normally to complete a closed circuit and in which upon heating of such thermostat said leaf will leave such closed circuit contact and will touch open circuit contacts in order to complete an open circuit from alternative lines; means, characterized in this, that said closed circuit contact also forms one of the said open circuit contacts, said other open circuit contact located upon the other side of the said leaf at such a position as to form a fulcrum for the leaf whereby as the thermostat arm continues moving the front end of said leaf will bend so as to again touch said closed circuit contact, an end wall to said thermostat, said contacts supported from terminals located in and insulated from said end wall, substantiall as described.

4. In an electrical re alarm thermostat havin an arm operable by the heating 0 said t ermostat, a tube, a rod within said tube which upon the expansion of said tube, will move backwards and operate said arm which is adapted to make and break contact with electrical contacts; means, characterized in this, that the said thermostat arm consists of a blade of thin material fixed to the thermostat base, and normally retained in position b said red but as said rod moves backwards t 0 said blade moves laterally against its own tension, a member -project ing from the side of said blade, the end of said rod being spherical in form, and engagin in a correspondingly shaped hole in sai member, substantia In testimony whereof, I have signed my name to this specification in the presence of two subscribin witnesses.

' TH S STOKER DIXON.

WitIBQSSTOB 017mm, A. Downs...

1y as described. 35 

